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First post, by King_Corduroy

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Hi guys I was wondering what the best route is for replacing one of these Nicad rechargeable batteries for older motheboards. I recently (as in today) picked up a 486dx Unix server tower and I need to replace this battery. Also is it safe to boot without the Cmos battery like on a newer pc?

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Reply 1 of 20, by smeezekitty

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It is safe to boot it without it. It will probably work fine but won't retain settings and clock over a reboot.
A few boards fail post without a battery but I have never heard of damage.

Does your board have an external battery connection?

Reply 2 of 20, by King_Corduroy

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I really don't know, this is my first time owning a computer like this. I've messed with older 8088 computers but nothing like this. 😒

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Reply 3 of 20, by King_Corduroy

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I've tried to power it on but I can't seem to get any video from it, it's monochrome and uses a 9 pin port. I don't think it's the monitor but I really have no idea where to start here. Any advice would be great. Could the lack of a battery be stopping this system from booting?

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Reply 4 of 20, by Artex

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See if you can dig up the motherboard info. It may have a 4 pin external battery header (and usually a jumper to enable it), and you can just hook up a battery that way.

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Reply 5 of 20, by feipoa

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Unlikely. Did you check for damaged PCB traces around the battery?

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Reply 6 of 20, by King_Corduroy

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let me look at it a little closer, but there shouldn't be, the battery was only just starting to explode and I did a really neat job of removing it (it took no effort at all with the new desoldering iron I picked up recently!).

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Reply 7 of 20, by HighTreason

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Nickel Cadmium? Those are rechargeable right?

If you don't have a jumper for an external one you can use a couple of AA batteries in a holder, but you will have to solder in a diode between the battery holder and the terminals where the old battery connected to prevent the board trying to charge them.

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Reply 8 of 20, by King_Corduroy

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looks as though there may be a little corrosion on a trace that was under the battery.

sam_0552_v01_by_mad_king_corduroy-d8iq11a.jpg

I was poking around the board looking for a manufacturer and noticed this:

sam_0555_v01_by_mad_king_corduroy-d8iq11i.jpg

It looks like its by Micronics Inc. But since I was able to remove the battery without removing the motherboard (there was an cutaway spot on the frame that allowed me to desolder it from the back.) I haven't as of yet taken everything off of it to allow me to see all parts of the mobo and be able to locate a model number.

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Reply 9 of 20, by Artex

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J11 in that first pic is the external battery header.

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Reply 10 of 20, by tincup

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Nice call Artex!

Reply 11 of 20, by King_Corduroy

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Ok cool, is there anything I need to know about getting one of those an hooking it up or will it simply be good to go.

Of course I'm still having issues getting the computer to do anything though. It doesn't seem to be booting really, the drive light comes on but it never checks the floppy drive or the tape drive so I assume it simply is not booting and that's why I have no video out.

I'm going to remove a few of the cards that were for serial terminal connections and things. (it was a Unix server)

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Reply 12 of 20, by Artex

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Yeah, with situations like these it's best to start bare-bones, taking all unnecessary cards out. Make sure everything is seated properly after a thorough examination of the board and components (especially capacitors). Take a look at the memory and see what kind its using - 30pin, 72pin, single sided, double sided, 60ns, 70ns, ECC, Non-ECC? Try swapping the memory if you have some laying around.

Is the video onboard? If so, maybe you could try throwing a discrete video card in there (ISA, or VLB if the board supports it), and see if you can get video that way. Here again, a jumper may be needed to enable/disable the onboard video controller if it has one.

I usually replace the older AT power supplies with a newer ATX one, using an ATX to AT converter cable. The last thing I want is an exploding PSU or a situation where the PSU destroys something else.

As far as the battery is concerned, I use these battery packs in at least 3 or 4 system and they've worked just fine. I've just used Velcro strips to stick the battery somewhere in the case - within reach, but out of the way of wires and other components. The jumper to enable it is most likely one of the ones real close to that battery header (or there is the off-chance that it may just... work!).

You've already taken care of that battery which is absolutely vital. I don't see too much corrosion there, but if you want you can take some vinegar and rub a little on areas where you see corrosion. This should neutralize the acid, and a toothbrush does a good job of getting the acid corrosion 'cruddies' off the board.

This looks similar to your board layout (at least from your pics):
http://museum.ttrk.ee/th99/m/M-O/32131.htm

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Reply 13 of 20, by smeezekitty

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King_Corduroy wrote:
looks as though there may be a little corrosion on a trace that was under the battery. […]
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looks as though there may be a little corrosion on a trace that was under the battery.

sam_0552_v01_by_mad_king_corduroy-d8iq11a.jpg

That one trace is suspect. Can you find the endpoints and check it with an ohm meter?

Reply 14 of 20, by Artex

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Hopefully it's just surface corrosion and can be scraped / cleaned away.

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Reply 15 of 20, by King_Corduroy

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No the motherboard lacks any connectors or controllers from what I can see, the floppy diskette drive is plugged into a really slim ISA card and the video card (or what I assume to be the video card since nothing is clearly marked) is an ISA card as well. It also has a serial card for a mouse (I assume) and the card which controls and communicates with the WYSE 50 serial terminals.

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Reply 16 of 20, by King_Corduroy

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Unfortunately I don't have any tools for electrical work at this time. 😒 I'll have to get a reliable and inexpensive multimeter.

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Reply 17 of 20, by King_Corduroy

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Artex I think you were right about the board, however on that page I don't seem to see any jumpers for setting the external battery.

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Also I've removed just about everything and it still does not boot.

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Reply 18 of 20, by feipoa

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-Try a different PSU
-Try a different video card
-Ensure all jumpers are setup accordingly. I have received boards which supposedly just came out of service with incorrectly set jumpers
-Remove all RAM and check for corrosion
-Try different RAM
-Try a different 486 CPU
-Try to clear the CMOS
-Try to read the BIOS with a stand-alone programmer and verify contents with a BIOS image found online for this board.
-Try to reseat the BIOS
-Try to reseat the chipset (CHIPS)

It is not essential to insert a diode to whatever battery you decide to use the barrel battery's leads. Instead, I prefer to disconnect the motherboard's diode which connects the battery to the point of charge, as shown in this photo,

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Reply 19 of 20, by King_Corduroy

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Thanks for the help! Unfortunately I can't do suggestions 1,2,5 and 6 since I don't have any more of this type of ram or other compatible parts. I am going to try and make myself a CMOS battery by wiring a CR2032 to a 4 pin floppy diskette power lead clipped from a cheap power supply (which I already checked and it does fit.). I'll look at it some more tomorrow.

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